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Abstract:

Provided is a display device including a photo sensor and a driving
method. The display device includes a first sensing unit and a second
sensing unit that sense light, at least one sensing signal line that is
connected with the first sensing unit and the second sensing unit and
transmits a reference voltage for resetting the first sensing unit and
the second sensing unit, a sensing signal processor that processes a
sensing signal from the sensing signal line, and a backlight that
irradiates internal light toward the first sensing unit and the second
sensing unit during an internal light irradiation period which is
repeated per frame, in which the first sensing unit is reset once and the
second sensing unit is reset at least three times during each frame.

Claims:

1. A display device, comprising: a first sensing unit and a second
sensing unit each configured to sense light; at least one sensing signal
line that is connected with the first sensing unit and the second sensing
unit and that is configured to transmit a reference voltage for resetting
the first sensing unit and the second sensing unit; a sensing signal
processor configured to process a sensing signal from the sensing signal
line; and a backlight configured to irradiate internal light toward the
first sensing unit and the second sensing unit during an internal light
irradiation period which is repeated per frame, wherein the first sensing
unit is reset once and the second sensing unit is reset at least three
times during each frame.

2. The display device of claim 1, wherein: the first sensing unit is
reset during a first output period which does not overlap the internal
light irradiation period, so as to output the sensing signal to the
sensing signal line.

3. The display device of claim 2, wherein: the second sensing unit is
reset in at least one preceding reset period, a main reset period, and a
second output period which occur sequentially.

4. The display device of claim 3, wherein: the second output period and
the main reset period do not overlap the internal light irradiation
period.

5. The display device of claim 4, wherein: a first sensing period, that
is between two adjacent first output periods, overlaps the internal light
irradiation period, and a second sensing period, that is between the main
reset period and an adjacent one of the second output periods, does not
overlap the internal light irradiation period.

6. The display device of claim 5, further comprising: a first scanning
signal line configured to transmit a scanning signal to the first sensing
unit; and a second scanning signal line configured to transmit a scanning
signal to the second sensing unit, wherein each of the first sensing unit
and the second sensing unit includes a switching element connected with
the first scanning signal line or the second scanning signal line, and a
sensing element and a capacitor that are connected with the switching
element, and wherein when the first sensing unit or the second sensing
unit is reset, the reference voltage is transmitted to the sensing
element and the capacitor through the switching element.

7. The display device of claim 6, wherein: an input terminal of the
sensing element included in the first sensing unit is connected with a
first source voltage line configured to transmit a predetermined first
voltage, and an input terminal of the sensing element included in the
second sensing unit is connected with a second source voltage line
configured to transmit the first voltage and a second voltage which is
different from the first voltage.

8. The display device of claim 7, wherein: a first period, in which a
voltage of the second source voltage line is the second voltage, overlaps
the internal light irradiation period.

9. The display device of claim 8, wherein: the second voltage is
substantially equal to the reference voltage.

10. The display device of claim 1, wherein: the second sensing unit is
reset in at least one preceding reset period, a main reset period, and a
second output period which occur sequentially.

11. The display device of claim 10, wherein: the second output period and
the main reset period do not overlap the internal light irradiation
period.

12. The display device of claim 1, further comprising: a first scanning
signal line configured to transmit a scanning signal to the first sensing
unit; and a second scanning signal line configured to transmit a scanning
signal to the second sensing unit, wherein each of the first sensing unit
and the second sensing unit includes a switching element connected with
the first scanning signal line or the second scanning signal line, and a
sensing element and a capacitor that are connected with the switching
element, and wherein when the first sensing unit or the second sensing
unit is reset, the reference voltage is transmitted to the sensing
element and the capacitor through the switching element.

13. The display device of claim 12, wherein: an input terminal of the
sensing element included in the first sensing unit is connected with a
first source voltage line configured to transmit a predetermined first
voltage, and an input terminal of the sensing element included in the
second sensing unit is connected with a second source voltage line
configured to transmit the first voltage and a second voltage which is
different from the first voltage.

14. The display device of claim 13, wherein: a first period, in which
voltage of the second source voltage line is the second voltage, overlaps
the internal light irradiation period.

15. The display device of claim 13, wherein: the second voltage is
substantially equal to the reference voltage.

16. A method of driving a display device including a first sensing unit
and a second sensing unit each configured to sense light, and at least
one sensing signal line connected with the first sensing unit and the
second sensing unit, the method comprising: irradiating light from the
display device toward the first sensing unit and the second sensing unit
during an internal light irradiation period which is repeated for each of
a number of frames; resetting the first sensing unit once during one
frame, so as to transmit a reference voltage transmitted from the sensing
signal line to the first sensing unit; and resetting the second sensing
unit at least three times during one frame, so as to transmit the
reference voltage to the second sensing unit.

17. The driving method of a display device of claim 16, wherein: the
resetting the first sensing unit is performed during a first output
period which does not overlap the internal light irradiation period.

18. The driving method of a display device of claim 17, wherein: the
resetting the second sensing unit is performed in at least one preceding
reset period, a main reset period, and a second output period which occur
sequentially.

19. The driving method of a display device of claim 18, wherein: the
second output period and the main reset period do not overlap the
internal light irradiation period.

20. The driving method of a display device of claim 19, wherein: a first
sensing period, that is between two adjacent first output periods,
overlaps the internal light irradiation period, and a second sensing
period, that is between the main reset period and an adjacent one of the
second output periods, does not overlap the internal light irradiation
period.

21. The driving method of a display device of claim 20, wherein the
display device further includes: a first scanning signal line configured
to transmit a scanning signal to the first sensing unit, and a second
scanning signal line configured to transmit a scanning signal to the
second sensing unit, wherein each of the first sensing unit and the
second sensing unit includes a switching element connected with the first
scanning signal line or the second scanning signal line, and a sensing
element and a capacitor that are connected with the switching element,
and wherein when the first sensing unit or the second sensing unit is
reset, the reference voltage is transmitted to the sensing element and
the capacitor through the switching element.

22. The driving method of a display device of claim 21, wherein: an input
terminal of the sensing element included in the first sensing unit is
connected with a first source voltage line configured to transmit a
predetermined first voltage, and an input terminal of the sensing element
included in the second sensing unit is connected with a second source
voltage line configured to transmit the first voltage and a second
voltage which is different from the first voltage.

23. The driving method of a display device of claim 22, wherein: a first
period, in which a voltage of the second source voltage line is the
second voltage, overlaps the internal light irradiation period.

24. The driving method of a display device of claim 23, wherein: the
second voltage is substantially equal to the reference voltage.

25. The driving method of a display device of claim 16, further
comprising: a first scanning signal line configured to transmit a
scanning signal to the first sensing unit; and a second scanning signal
line configured to transmit a scanning signal to the second sensing unit,
wherein each of the first sensing unit and the second sensing unit
includes a switching element connected with the first scanning signal
line or the second scanning signal line, and a sensing element and a
capacitor that are connected with the switching element, and wherein when
the first sensing unit or the second sensing unit is reset, the reference
voltage is transmitted to the sensing element and the capacitor through
the switching element.

26. The driving method of a display device of claim 25, wherein: an input
terminal of the sensing element included in the first sensing unit is
connected with a first source voltage line configured to transmit a
predetermined first voltage, and an input terminal of the sensing element
included in the second sensing unit is connected with a second source
voltage line configured to transmit the first voltage and a second
voltage which is different from the first voltage.

27. The driving method of a display device of claim 26, wherein: a first
period, in which a voltage of the second source voltage line is the
second voltage, overlaps the internal light irradiation period.

28. The driving method of a display device of claim 26, wherein: the
second voltage is substantially equal to the reference voltage.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to, and the benefit of, Korean
Patent Application No. 10-2012-0032639 filed in the Korean Intellectual
Property Office on Mar. 29, 2012, the entire contents of which are
incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] (a) Field of the Invention

[0003] Embodiments of the present invention relate generally to flat panel
displays. More specifically, embodiments of the present invention relate
to a display device including a photo sensor and a driving method
therefor.

[0004] (b) Description of the Related Art

[0005] Various kinds of flat panel displays have been developed for
various uses. Particularly, display devices having a touch sensing
function or an image sensing function have been developed.

[0006] In general, touch-sensitive displays often employ a touch screen
panel capable of sensing a contact, where this panel is attached to the
display device. However, such configurations often suffer from high cost,
yield reduction due to addition of an adhesion process, luminance
deterioration of the display panel, and the like. Accordingly, a
technology for embedding a sensor into the display area of the display
device has been developed. The embedded sensor often employs a thin film
transistor or capacitor, outputs a sensing signal according to change in
irradiated light due to an external contact and the like, and determines
contact information such as a contact position of an object, intensity of
contact, and the like by using the sensing signal.

[0007] One such sensor is a photo sensor, i.e. a sensor sensing change in
light, which may generate a sensing signal by using photocurrent
generated by incident light and may acquire contact information by using
the sensing signal. The light sensed by the sensor may be lights having
various frequencies such as infrared light, visible light, and the like,
and a light source generating the light sensed by the sensor may be
positioned in the display device. For example, a backlight, which is an
internal light source for displaying an image of the display device, may
be configured so as to emit light having a wavelength suitable for the
photo sensor in addition to visible light. However, the photo sensor may
be influenced by light from an additional exterior light source and as a
result, inexact contact information may be acquired.

[0008] Furthermore, photo sensors typically employ a photosensitive
transistor. This transistor is a three-terminal element that determines
whether or not contact exists via a photocurrent formed by irradiating
light upon the channel part of the transistor. However, even when no
light shines upon the photo sensor, photo leakage current may be present
and, as a result, an error in the contact information may occur.

[0009] The above information disclosed in this Background section is only
for enhancement of understanding of the background of the invention and
therefore it may contain information that does not form the prior art
that is already known in this country to a person of ordinary skill in
the art.

SUMMARY OF THE INVENTION

[0010] The present invention has been made in an effort to provide a
display device including a photo sensor capable of obtaining more precise
contact information, as well as a driving method therefor.

[0011] An exemplary embodiment of the present invention provides a display
device, including: a first sensing unit and a second sensing unit each
configured to sense light, at least one sensing signal line that is
connected with the first sensing unit and the second sensing unit and
that is configured to transmit a reference voltage for resetting the
first sensing unit and the second sensing unit, a sensing signal
processor configured to process a sensing signal from the sensing signal
line, and a backlight configured to irradiate internal light toward the
first sensing unit and the second sensing unit during an internal light
irradiation period which is repeated per frame, in which the first
sensing unit is reset once and the second sensing unit is reset at least
three times during each frame.

[0012] The first sensing unit may be reset during a first output period
which does not overlap the internal light irradiation period so as to
output the sensing signal to the sensing signal line.

[0013] The second sensing unit may be reset in at least one preceding
reset period, a main reset period, and a second output period which occur
sequentially.

[0014] The second output period and the main reset period may or may not
overlap the internal light irradiation period.

[0015] A first sensing period, that is between two adjacent first output
periods for the first sensing unit, may overlap the internal light
irradiation period, and a second sensing period, that is between the main
reset period and an adjacent one of the second output periods, may not
overlap the internal light irradiation period.

[0016] The display device may further include a first scanning signal line
configured to transmit a scanning signal to the first sensing unit; and a
second scanning signal line configured to transmit a scanning signal to
the second sensing unit. Each of the first sensing unit and the second
sensing unit may include a switching element connected with the first
scanning signal line or the second scanning signal line, and a sensing
element and a capacitor that are connected with the switching element.
When the first sensing unit or the second sensing unit is reset, the
reference voltage may be transmitted to the sensing element and the
capacitor through the switching element.

[0017] An input terminal of the sensing element included in the first
sensing unit may be connected with a first source voltage line configured
to transmit a predetermined first voltage, and an input terminal of the
sensing element included in the second sensing unit may be connected with
a second source voltage line configured to transmit the first voltage and
a second voltage which is different from the first voltage.

[0018] A first period, in which a voltage of the second source voltage
line is the second voltage, may overlap the internal light irradiation
period.

[0019] The second voltage may be substantially equal to the reference
voltage.

[0020] Another exemplary embodiment of the present invention provides a
method of driving a display device including a first sensing unit and a
second sensing unit each configured to sense light, and at least one
sensing signal line connected with the first sensing unit and the second
sensing unit. The method includes: irradiating light from the display
device toward the first sensing unit and the second sensing unit during
an internal light irradiation period which is repeated for each of a
number of frames; resetting the first sensing unit once during one frame
so as to transmit a reference voltage transmitted from the sensing signal
line to the first sensing unit; and resetting the second sensing unit at
least three times during one frame so as to transmit the reference
voltage to the second sensing unit.

[0021] The resetting the first sensing unit may be performed during a
first output period which does not overlap the internal light irradiation
period.

[0022] The resetting the second sensing unit may be performed in at least
one preceding reset period, a main reset period, and a second output
period which occur sequentially.

[0023] The second output period and the main reset period may not overlap
the internal light irradiation period.

[0024] A first sensing period, that is between two adjacent first output
periods, may overlap the internal light irradiation period, and a second
sensing period, that is between the main reset period and an adjacent one
of the second output periods, may not overlap the internal light
irradiation period.

[0025] The display device may further include a first scanning signal line
configured to transmit a scanning signal to the first sensing unit, and a
second scanning signal line configured to transmit a scanning signal to
the second sensing unit. Each of the first sensing unit and the second
sensing unit may include a switching element connected with the first
scanning signal line or the second scanning signal line, and a sensing
element and a capacitor that are connected with the switching element.
When the first sensing unit or the second sensing unit is reset, the
reference voltage may be transmitted to the sensing element and the
capacitor through the switching element.

[0026] An input terminal of the sensing element included in the first
sensing unit may be connected with a first source voltage line configured
to transmit a predetermined first voltage, and an input terminal of the
sensing element included in the second sensing unit may be connected with
a second source voltage line configured to transmit the first voltage and
a second voltage which is different from the first voltage.

[0027] A first period, in which a voltage of the second source voltage
line is the second voltage, may overlap the internal light irradiation
period.

[0028] The second voltage may be substantially equal to the reference
voltage.

[0029] According to the exemplary embodiments of the present invention, it
is possible to acquire more exact contact information in which noise due
to exterior light is substantially removed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a block diagram of a display device including a photo
sensor according to an exemplary embodiment of the present invention.

[0031] FIG. 2 is a circuit diagram of a photo sensor or a sensing unit
according to the exemplary embodiment of the present invention.

[0032]FIG. 3 is a circuit diagram of a sensing signal processor according
to the exemplary embodiment of the present invention.

[0033]FIG. 4 is a cross-sectional view of a display device including a
photo sensor according to the exemplary embodiment of the present
invention.

[0034] FIG. 5 is a block diagram of a display device including a photo
sensor according to the exemplary embodiment of the present invention.

[0035] FIG. 6 is a timing diagram illustrating a driving method of a
display device including a photo sensor according to another exemplary
embodiment of the present invention.

[0036]FIG. 7 is another example of a timing diagram illustrating a
driving method of a display device including a photo sensor according to
another exemplary embodiment of the present invention.

[0037]FIG. 8 is another example of a timing diagram illustrating a
driving method of a display device including a photo sensor according to
another exemplary embodiment of the present invention.

[0038]FIG. 9 is a layout view of a photo sensor according to the
exemplary embodiment of the present invention.

[0039] FIG. 10 is another example of a timing diagram illustrating a
driving method of a display device including a photo sensor according to
another exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The present invention will be described more fully hereinafter with
reference to the accompanying drawings, in which exemplary embodiments of
the invention are shown. As those skilled in the art would realize, the
described embodiments may be modified in various different ways, all
without departing from the spirit or scope of the present invention.

[0041] In the drawings, the thickness of layers, films, panels, regions,
etc., are exaggerated for clarity. Like reference numerals designate like
elements throughout the specification. It will be understood that when an
element such as a layer, film, region, or substrate is referred to as
being "on" another element, it can be directly on the other element or
intervening elements may also be present. In contrast, when an element is
referred to as being "directly on" another element, there are no
intervening elements present.

[0042] First, a display device including a photo sensor according to an
exemplary embodiment of the present invention will be described with
reference to FIGS. 1 to 4.

[0043] FIG. 1 is a block diagram of a display device including a photo
sensor according to an exemplary embodiment of the present invention,
FIG. 2 is a circuit diagram of a photo sensor or a sensing unit according
to the exemplary embodiment of the present invention, FIG. 3 is a circuit
diagram of a sensing signal processor according to the exemplary
embodiment of the present invention, and FIG. 4 is a cross-sectional view
of a display device including a photo sensor according to the exemplary
embodiment of the present invention.

[0044] Referring to FIG. 1, a touch-sensitive display device according to
an exemplary embodiment of the present invention includes a sensing area
SA, a backlight 900, a scan driver 400, and a sensing signal processor
500.

[0045] The sensing area SA is an area capable of sensing a change in light
due to touch or access of an external object. The sensing area SA
includes a plurality of scanning signal lines Ga1, Gb1, Gc1, Gd1, Ga2,
Gb2, Gc2, Gd2, . . . , a plurality of sensing signal lines RO1, RO2, . .
. , and a plurality of sensing unit groups SU (also referred to as sensor
groups) which are arranged substantially in a matrix form.

[0046] The sensing area SA may correspond to a display area (not shown) in
which a plurality of pixels (not shown) disposed on a display panel of
the display device are arranged. The plurality of pixels may be connected
to a plurality of image scanning signal lines transmitting scanning
signals for displaying an image, and image data lines transmitting image
data signals.

[0047] The plurality of scanning signal lines (also referred to as "gate
lines") transmit the scanning signals (alternately, gate signals) and may
extend substantially in a row direction. The plurality of scanning signal
lines Ga1, Gb1, Gc1, Gd1, Ga2, Gb2, Gc2, Gd2, . . . may be divided into a
plurality of scanning signal line groups which may independently transmit
the scanning signals in sequence. In detail, the plurality of scanning
signal lines Ga1, Gb1, Gc1, Gd1, Ga2, Gb2, Gc2, Gd2, . . . may include a
first scanning signal line group (Ga1, Ga2, . . . ), a second scanning
signal line group (Gb1, Gb2, . . . ), a third scanning signal line group
(Gc1, Gc2, . . . ), and a fourth scanning signal line group (Gd1, Gd2, .
. . ). The scanning signals of the first scanning signal line group (Ga1,
Ga2, . . . ), the second scanning signal line group (Gb1, Gb2, . . . ),
the third scanning signal line group (Gc1, Gc2, . . . ), and the fourth
scanning signal line group (Gd1, Gd2, . . . ) may be sequentially and
alternately arranged, as shown in FIG. 1.

[0048] In the exemplary embodiment shown in FIG. 1, the four kinds of
scanning signal line groups are shown, but the layout and distribution of
the scanning signal line groups is not limited thereto and may, for
example, be configured with two kinds or more of scanning signal line
groups.

[0050] Each sensing unit group SU may include at least two sensing units
or photo sensors. FIG. 1 shows an example in which one sensing unit group
SU includes four kinds of sensing units SUa, SUb, SUc, and SUd. Different
kinds of sensing units SUa, SUb, SUc, and SUd included in each sensing
unit group SU may be independently driven to output the sensing signals.

[0051] The sensing units SUa, SUb, SUc, and SUd included in one sensing
unit group SU may be disposed in a generally quadrangular shape as shown
in FIG. 1. However, the four sensing units SUa, SUb, SUc, and SUd
included in one sensing unit group SU may may be arranged in various
other layouts or shapes. For example, the sensing units SUa, SUb, SUc,
and SUd included in one sensing unit group SU may also be arranged in a
line in a column direction or row direction.

[0052] The plurality of sensing units SUa, SUb, SUc, and SUd include a
first sensing unit SUa connected with the first scanning signal line
group (Ga1, Ga2, . . . ), a second sensing unit SUb connected with the
second scanning signal line group (Gb1, Gb2, . . . ), a third sensing
unit SUc connected with the third scanning signal line group (Gc1, Gc2, .
. . ), and a fourth sensing unit SUd connected with the fourth scanning
signal line group (Gd1, Gd2, . . . ).

[0053] The scanning signal lines Ga1, Gb1, Gc1, Gd1, Ga2, Gb2, Gc2, Gd2, .
. . may be disposed two by two for every one sensing unit row. For
example, one scanning signal line of the first scanning signal line group
(Ga1, Ga2, . . . ) and one scanning signal line of the second scanning
signal line group (Gb1, Gb2, . . . ) may be disposed directly on or
beneath the sensing unit row in which the first and second sensing units
SUa and SUb are disposed, and one scanning signal line of the third
scanning signal line group (Gc1, Gc2, . . . ) and one scanning signal
line of the fourth scanning signal line group (Gd1, Gd2, . . . ) may be
disposed directly on or beneath the sensing unit row in which the third
and the fourth sensing units SUc and SUd are disposed.

[0054] However, the scanning signal lines Ga1, Gb1, Gc1, Gd1, Ga2, Gb2,
Gc2, Gd2, . . . may also be disposed by ones or twos or more for every
one sensing unit.

[0055] The sensing signal lines RO1, RO2, . . . may be disposed by ones
for every one sensing unit SU column. In this case, the plurality of
sensing units SUa, SUb, SUc, and SUd included in one sensing unit group
SU may be connected to the same sensing signal line from among RO1, RO2,
. . . . Further, as shown in FIG. 1, the same sensing signal lines RO1,
RO2, . . . may extend to pass between the sensing units SUa, SUb, SUc,
and SUd included in each sensing unit group SU. However, the sensing
signal lines are not limited thereto and may also extend in a column
direction from the left side or right side of the sensing unit group SU.

[0056] Unlike the configuration shown in FIG. 1, a plurality of sensing
signal lines may be positioned per a sensing unit group SU column, and at
least two of the sensing units SUa, SUb, SUc, and SUd included in one
sensing unit group SU may also be connected to different sensing signal
lines.

[0057] The sensing units SUa, SUb, SUc, and SUd may be photo sensors
generating the sensing signals by sensing a touch or access of an
external object, or sensing an image of the external object by using
internal light IL generated from the backlight 900. For example, the
sensing units SUa, SUb, SUc, and SUd may also sense a touch from an
external object by using infrared light, or by using visible light.

[0058] Referring to FIG. 2, a sensing unit SUk (k=a, b, c, d, . . . )
according to an exemplary embodiment of the present invention may be one
of the sensing units SUa, SUb, SUc, and SUd described above. The sensing
unit SUk may include a switching element Qa connected with a scanning
signal line Gi and a sensing signal line ROj, and a sensing element Qs
and a capacitor Cs connected with the switching element Qa.

[0059] The switching element Qa is a three-terminal element such as a thin
film transistor or the like, where a control terminal thereof is
connected with the scanning signal line Gi, an output terminal is
connected with the sensing signal line ROj (j=1 2, . . . ), and an input
terminal is connected with the sensing element Qs and the capacitor Cs.
The scanning signal line Gi may be any one of the first scanning signal
line group (Ga1, Ga2, . . . ), the second scanning signal line group
(Gb1, Gb2, . . . ), the third scanning signal line group (Gc1, Gc2, . . .
), and the fourth scanning signal line group (Gd1, Gd2, . . . ) described
above, or a sub scanning signal line connected therewith. The switching
element Qa may transmit the sensing signal to the sensing signal line ROj
according to the scanning signal of the scanning signal line Gi.

[0060] Referring to FIG. 2A, the sensing element Qs according to the
exemplary embodiment of the present invention is a three-terminal element
such as a thin film transistor or the like, where an input terminal
thereof receives a source voltage Vs (also referred to as "a first
voltage"), a control terminal receives a bias voltage Vb (also referred
to as "a second voltage"), and an output terminal is connected with the
switching element Qa. The bias voltage Vb may be a sufficiently low or
high voltage, like a gate-off voltage, that the sensing element Qs is
kept in an off state when the light is not irradiated upon the sensing
element Qs.

[0061] Referring to FIG. 2B, the sensing element Qs according to another
exemplary embodiment may receive the bias voltage Vb at both its input
terminal and its control terminal, unlike the exemplary embodiment shown
in FIG. 2A.

[0062] That is, the sensing element Qs may be diode-connected. Even in
this case, the bias voltage Vb may be a sufficiently low or high voltage,
like a gate-off voltage, that the sensing element Qs is kept in an off
state when the light is not irradiated upon the sensing element Qs.

[0063] The sensing element Qs may include a photoelectric material
generating photo (leakage) current when the light is irradiated. An
example of the sensing element Qs may include a thin film transistor
having an amorphous silicon, amorphous silicon-germanium, or polysilicon
channel which can generate the photocurrent. The light irradiated upon
the sensing element Qs may include exterior light in addition to the
internal light IL from the backlight 900.

[0064] In the configuration of FIG. 2a, two terminals of the capacitor Cs
are connected to the switching element Qa and the source voltage Vs,
respectively. The capacitor Cs may be charged to the reference voltage Vf
applied to the sensing signal line ROj according to the scanning signal
of the scanning signal line Gi, or be discharged according to the
photocurrent of the sensing element Qs.

[0065] The backlight 900 generates the internal light IL such as infrared
light, visible light, and the like. The backlight 900 is disposed at the
rear side of the display device and generates the internal light IL to be
irradiated upon the plurality of sensing units SUa, SUb, SUc, and SUd.
For example, the exemplary embodiment of the present invention may use
the backlight 900 to generate the infrared light used for sensing the
touch of the external object. In this case, when the external object is
close to the display device or the sensing area SA, the infrared light
from the backlight 900 is reflected from the external object back toward
(i.e., to be inputted to) the sensing units SUa, SUb, SUc, and SUd. On
the contrary, in the case of using a visible light backlight 900, when
the external object is close to the display device or the sensing area
SA, the visible light from the backlight 900 is reflected from the
external object to be inputted to the sensing units SUa, SUb, SUc, and
SUd.

[0066] The photo sensor according to the exemplary embodiment of the
present invention may sense a kind of light, but may include a plurality
of sensing units sensing light having different wavelength bands. For
example, one display device may also include an infrared light sensing
unit capable of sensing infrared light and a visible light sensing unit
capable of sensing visible light. In this case, the infrared light
sensing unit and the visible light sensing unit may be alternately
arranged.

[0067] Referring back to FIG. 1, the scan driver 400 is connected to the
scanning signal lines Ga1, Gb1, Gc1, Gd1, Ga2, Gb2, Gc2, Gd2, . . . . The
scan driver 400 applies scanning signals which include a combination of a
gate-on voltage for turning on the switching element Qa of each of the
sensing units SUa, SUb, SUc, and SUd, and a gate-off voltage for turning
off the switching elements Qa thereof.

[0068] The scan driver 400 may independently transmit the scanning signals
to each of the first scanning signal line group (Ga1, Ga2, . . . ), the
second scanning signal line group (Gb1, Gb2, . . . ), the third scanning
signal line group (Gc1, Gc2, . . . ), and the fourth scanning signal line
group (Gd1, Gd2, . . . ),

[0069] For example, the scan driver 400 may receive a plurality of gate
clock signals for controlling output timings of gate-on pulses of the
scanning signal line groups (Ga1, Gb1, Gc1, Gd1, Ga2, Gb2, Gc2, Gd2, . .
. ), respectively. Accordingly, the first scanning signal line group
(Ga1, Ga2, . . . ), the second scanning signal line group (Gb1, Gb2, . .
. ), the third scanning signal line group (Gc1, Gc2, . . . ), and the
fourth scanning signal line group (Gd1, Gd2, . . . ) may independently
transmit the gate-on voltages at different times or at the same time.
Further, the plurality of scanning signal lines included in one scanning
signal line group may sequentially output each gate-on voltage for a
predetermined time unit. In this case, the predetermined time unit may be
1 horizontal period 1H.

[0070] The sensing signal processor 500 is connected with the sensing
signal lines RO1, RO2, . . . . The sensing signal processor 500 may
receive the sensing signals from the sensing signal lines RO1, RO2, . . .
to process the received sensing signals and then generate contact
information such as whether there is a contact or not, a contact
position, shape and size of a contact object.

[0071] Referring to FIG. 3, the sensing signal processor 500 according to
the exemplary embodiment of the present invention may include an
integrator connected to the sensing signal line ROj (j=1, 2, . . . ).
Each integrator may include an amplifier AP having an inversion terminal
(-), a non-inversion terminal (+) and an output terminal, and a capacitor
Cf connected thereto. The inversion terminal (-) of the amplifier AP is
connected to the sensing signal line RO, and the capacitor Cf is
connected between the inversion terminal (-) and the output terminal. The
non-inversion terminal (+) of the amplifier AP is connected to the
reference voltage Vf. In more detail, the amplifier AP and the capacitor
Cf are current integrators and may integrate current of the sensing
signal from the sensing signal line ROj to generate a sensing output
signal Vout.

[0072] Referring to FIG. 4, a display panel 300 of the display device
according to the exemplary embodiment of the present invention may
include two display panels 100 and 200 which face each other, and an
intermediate layer 3 disposed therebetween. The sensing unit group SU
according to the exemplary embodiment of the present invention may be
disposed at a lower panel 100 or an upper panel 200. The intermediate
layer 3 may be a liquid crystal layer in the case of a liquid crystal
display, may be an electrophoretic layer including charged particles in
the case of an electrophoretic display, and may include fluids in the
case of an electro wetting display. On the contrary, in the case where a
display device includes one display panel like an organic light emitting
diode display, the sensing unit group SU may be disposed on the display
panel or disposed at an encapsulation substrate covering the display
panel.

[0073] The display device further includes backlight 900 disposed at the
bottom of the display panels 100 and 200, and the backlight 900
irradiates internal light IL toward the sensing unit group SU. In the
case where the external object is close to the display panel, the
internal light IL may be reflected from the external object to be
inputted to the sensing unit group SU and thus sensed. A light blocking
member 260 is disposed between the sensing unit group SU and the
backlight 900 to prevent the internal light IL from being directly
irradiated from the backlight 900 to the sensing unit group SU. In this
case, exterior light OL emitted from a source other than the backlight
900 may further be irradiated to the sensing unit group SU. More precise
contact information may be obtained through a process of removing an
effect due to the exterior light OL. The process will be described with
reference to a driving method to be described below.

[0074] Then, an operation of the photo sensor according to the exemplary
embodiment of the present invention will be described with reference to
FIGS. 1 to 4.

[0075] First, the scan driver 400 applies a gate-on voltage Von to the
scanning signal lines Ga1, Gb1, Gc1, Gd1, Ga2, Gb2, Gc2, Gd2, . . . in
sequence to turn on the switching element Qa included in the sensing
units SUa, SUb, SUc, and SUd. Then, the reference voltage Vf applied to
the sensing signal lines RO1, RO2, . . . is transmitted to one terminal
of the capacitor Cs, and the capacitor Cs is charged by a difference
between the reference voltage Vf and the source voltage Vs. This process
is referred to as a reset step or a reset period of the sensing units
SUa, SUb, SUc, and SUd.

[0076] In a state where the switching element Qa is turned off, when light
is irradiated upon the sensing element Qs by the touch of an external
object or the like, a photocurrent is generated in the sensing element
Qs. Then, a voltage drop occurs in the terminal to which the reference
voltage Vf of the capacitor Cs is applied, and the capacitor Cs
discharges. On the contrary, when light is not irradiated upon the
sensing element Qs (i.e. no touch is occurring), the capacitor Cs is not
discharged. This process is referred to as a sensing step or a sensing
period of the sensing units SUa, SUb, SUc, and SUd.

[0077] At the next reset step, when the gate-on voltage Von is applied to
the scanning signal lines Ga1, Gb1, Gc1, Gd1, Ga2, Gb2, Gc2, Gd2, . . . ,
the switching element Qa is turned on. At the previous sensing step, when
a charged voltage of the capacitor Cs is changed due to the touch, the
reference voltage Vf is recharged to the reference voltage Vf through the
turned on switching element Qa. In this case, the current is generated to
the sensing signal lines RO1, RO2, . . . , the sensing signal is
generated and the sensing signal may be inputted to the sensing signal
processor 500 to be processed. This process is referred to as an output
step or an output period. Since the reset of the sensing unit and the
output of the sensing signal occur at the same time according to the
application of the scanning signal, the reset step may be the output
step.

[0078] Next, a display device including a photo sensor according to a
further exemplary embodiment of the present invention will be described
with reference to FIG. 5. Like reference numerals designate like
constituent elements as the exemplary embodiment described above and the
same description is omitted.

[0079] FIG. 5 is a block diagram of a display device including a photo
sensor according to a further exemplary embodiment of the present
invention.

[0080] Referring to FIG. 5, a display device including a photo sensor
according to this exemplary embodiment of the present invention is
similar to the exemplary embodiment shown in FIGS. 1 to 4, but the number
of sensing units included in one sensing unit group SU and kinds of
scanning signal lines may be different.

[0081] In more detail, a sensing area SA of the display device includes a
first scanning signal line group (Ga1, Ga2, . . . ) and a second scanning
signal line group (Gb1, Gb2, . . . ) which may independently transmit
scanning signals, a first sensing unit SUa connected to the first
scanning signal line group (Ga1, Ga2, . . . ), and a second sensing unit
SUb connected to the second scanning signal line group (Gb1, Gb2, . . .
).

[0082] The first sensing unit SUa and the second sensing unit SUb may be
alternately disposed in a row direction and a column direction. The first
sensing unit SUa and the second sensing unit SUb which are adjacent to
each other may form one sensing unit group SU described above. The
adjacent first sensing unit SUa and second sensing unit SUb may also be
connected to the same sensing signal line like the exemplary embodiment
shown in FIG. 1 and may also be connected to different sensing signal
lines (not shown).

[0083] In addition, various features of the exemplary embodiment shown in
FIGS. 1 to 4 described above may be equally applied thereto.

[0084] Next, a driving method of a display device including a photo sensor
according to another exemplary embodiment of the present invention will
be described with reference to FIGS. 1 to 5, and FIG. 6, but for
convenience of the description, the driving method will be described in
connection with the configuration shown in FIG. 5, i.e. a photo sensor
including two kinds of sensing units SUa and SUb.

[0085] FIG. 6 is a timing diagram illustrating a driving method of a
display device including a photo sensor according to another exemplary
embodiment of the present invention.

[0086] Referring to FIG. 6, the backlight 900 irradiates internal light IL
to the display device during an internal light irradiation period IL_ON
which is repeated for each frame. A time from a start point of one
internal light irradiation period IL_ON to a start point of the next
internal light irradiation period IL_ON corresponds to one frame, and a
period between the internal light irradiation periods IL_ON of the
adjacent frames is an internal light non-irradiation period. FIG. 6 shows
the N-th frame and part of the N-1-th and N+1-th frames which are
disposed at the front and the rear thereof.

[0087] First, in the first sensing unit SUa, a reset step and an output
step of the first sensing unit SUa may be performed at the same time. In
FIG. 6, a period corresponding to the reset step or the output step of
the first sensing unit SUa is represented by the same reference numeral
as the first sensing unit SUa and is called a reset period SUa or an
output period SUa. A period between the adjacent output periods SUa of
the first sensing unit SUa is called a sensing period SPa and has a
period corresponding to a sensing step of light. The sensing period SPa
shown in FIG. 6 is represented on the basis of the first sensing unit SUa
connected to a scanning signal line Ga1 which first receives the scanning
signal. The sensing period SPa of the first sensing unit SUa may continue
for substantially the duration of one frame.

[0088] One output period SUa of the first sensing unit SUa is positioned
between two adjacent internal light irradiation periods IL_ON. That is,
one output period SUa for the first sensing unit SUa is present in every
one frame to generate the sensing signal. The output period SUa of the
first sensing unit SUa does not overlap the internal light irradiation
period IL_ON, and may be disposed before the internal light irradiation
period IL_ON starts, as shown in FIG. 6.

[0089] In more detail, the capacitor Cs is recharged with the reference
voltage Vf and reset in the output period SUa of the first sensing unit
SUa in the N-1-th frame which is positioned before the internal light
irradiation period IL_ON of the N-th frame, and then the sensing period
SPa of the first sensing unit SUa proceeds. The sensing period SPa may be
continued for the same duration as one frame.

[0090] An internal light irradiation period IL_ON of the backlight 900 for
the N-th frame is disposed in the sensing period SPa of the first sensing
unit SUa. One sensing period SPa includes the internal light irradiation
period IL_ON and the following internal light IL non-irradiation period.
That is, the internal light irradiation period IL_ON may be continued
only during a part of the sensing period SPa of the first sensing unit
SUa. Only the exterior light OL may be irradiated to the second sensing
unit SUb during the internal light IL non-irradiation period of the
sensing period SPa.

[0091] The sensing period SPa of the first sensing unit SUa ends when the
output period SUa of the first sensing unit SUa of the N-th frame starts.
In the output period SUa of the first sensing unit SUa, the capacitor Cs
is recharged to the reference voltage Vf and simultaneously, the sensing
signal may be generated if the voltage of the capacitor Cs was changed
during the previous sensing period SPa. Thus, a contact occurring during
the previous sensing period SPa may be acquired during the current output
period SUa by using the sensing signal.

[0092] A duration time T1 of each output period SUa of the first sensing
unit SUa may be substantially the same as a time taken to apply a
scanning signal Vg_SUa to all the scanning signal lines Ga1, Gb1, Ga2,
Gb2, . . . of the sensing area SA in sequence, but is not limited thereto
and may also be longer than that time.

[0093] Meanwhile, during the sensing period SPa of the first sensing unit
SUa, noise may occur in the sensing signal due to the presence of
exterior light OL in addition to the internal light IL from the backlight
900. The second sensing unit SUb, which is adjacent or close to the first
sensing unit SUa, may be used to remove this noise. This will be
described below.

[0094] Next, the second sensing unit SUb is reset in at least three
periods of reset periods SUb_r and SUb_k and an output period SUb for one
frame to generate a sensing signal. That is, the second sensing unit SUb
is reset at least three times for one frame to generate the sensing
signal. However, in the exemplary embodiment of the present invention, a
period in which the sensing signal outputted from the second sensing unit
SUb is processed to acquire contact information is called the output
period SUb, and a period which is not so is called the reset periods
SUb_r and SUb_k (where k=a natural number, the same as above). In the
reset periods SUb_r and SUb_k, the capacitor Cs is charged to the
reference voltage Vf to reset the second sensing unit SUb without
generating the sensing signal or acquiring the contact information.

[0095] The output period SUb of the second sensing unit SUb is positioned
between adjacent internal light irradiation periods IL_ON and does not
overlap the internal light irradiation period IL_ON. That is, a time
distance T2 between the start point of the output period SUb of the
second sensing unit SUb and the end point of the internal light
irradiation period IL_ON may be 0 or more. The output period SUb of the
second sensing unit SUb may be positioned next to the output period SUa
of the first sensing unit SUa.

[0096] The reset periods SUb_r and SUb_k of the second sensing unit SUb
are positioned before the output period SUb in the corresponding frame.

[0097] In one frame, the reset periods SUb_r and SUb_k of the second
sensing unit SUb include one main reset period SUb_r and at least one
preceding reset period SUb_k. FIG. 6 shows an exemplary embodiment in
which three preceding reset periods SUb_1, SUb_2, and SUb_3 are included
in one frame.

[0098] The main reset period SUb_r is positioned as the last of the
plurality of reset periods SUb_r and SUb_k and, here, does not overlap
the internal light irradiation period IL_ON (although it may in other
embodiments). The main reset period SUb_r may be positioned in the
sensing period SPa of the first sensing unit SUa.

[0099] At least one of the preceding reset periods SUb_1, SUb_2, and SUb_3
precedes the main reset period SUb_r and each may be positioned in
sequence. In the exemplary embodiment shown in FIG. 6, the preceding
reset periods SUb_1, SUb_2, and SUb_3 may partially overlap the internal
light irradiation period IL_ON (here, the first two reset periods Sub_1
and Sub_2 each fully overlap IL_ON, while the third reset period Sub_3
partially overlaps IL_ON, but the invention encompasses embodiments with
any relative durations of SUb_1, SUb_2, Sub_3, and IL_ON).

[0100] In more detail, the second sensing unit SUb may be reset many times
through at least one of the preceding reset periods SUb_1, SUb_2, and
SUb_3 and one main reset period SUb_r before entering a sensing period
SPb which continues after the main reset period SUb_r ends. The sensing
period SPb shown in FIG. 6 is represented on the basis of the second
sensing unit SUb connected to a scanning signal line Gb1 which first
receives the scanning signal. Accordingly, since the second sensing unit
SUb is sufficiently reset before the sensing period SPb, the capacitor Cs
may be sufficiently charged to the reference voltage Vf and may
sufficiently remove charges remaining in the sensing element Qs.

[0101] The second sensing unit SUb may sense the exterior light OL during
the sensing period SPb starting after the main reset period SUb_r ends
for respective second sensing units SUb. In the case where exterior light
is present, the photocurrent flows from the sensing element Qs of the
second sensing unit SUb and the capacitor Cs of the second sensing unit
SUb may also be discharged. The sensing period SPb shown in FIG. 6 is
represented on the basis of the second sensing unit SUb connected to a
scanning signal line Gb1 which first receives the scanning signal. The
sensing period SPb of the second sensing unit SUb is smaller than one
frame. The sensing period SPb of the second sensing unit SUb ends when
the next output period SUb starts.

[0102] In the output period SUb of the second sensing unit SUb, while the
capacitor Cs of the second sensing unit SUb is recharged to the reference
voltage Vf, the sensing signal is generated according to the degree of
discharging that has occurred during the immediately preceding sensing
period SPb. The sensing signal of the second sensing unit SUb outputted
from the output period SUb may depend on the existence of the exterior
light OL or the intensity thereof.

[0103] In the exemplary embodiment, assuming that a difference in the
sensing signals of the second sensing unit SUb due to the exterior light
OL is mostly unrelated to the irradiation time of the exterior light OL,
when subtracting the sensing signal of the output period SUb of the
second sensing unit SUb from the sensing signal of the output period SUa
of the first sensing unit SUa, the above-described "noise" effect due to
exterior light OL may be mostly removed from the sensing signal of the
first sensing unit SUa. Accordingly, a sensing signal which is not
influenced by the exterior light OL may be acquired, and when the sensing
signal is processed to acquire contact information, more exact contact
information or a more exact image of the object may be obtained.

[0104] The duration time T1 of each of the reset periods SUb_r and SUb_k
and the output period SUb of the second sensing unit SUb may be
substantially the same as a time taken to apply a scanning signal Vg_SUb
to all the scanning signal lines Ga1, Gb1, Ga2, Gb2, . . . of the sensing
area SA in sequence, but is not limited thereto and may also be longer
than the time.

[0105] Meanwhile, in the case where the backlight 900 supplies the
internal light IL together with the visible light to the display panel of
the display device, one frame shown in FIG. 6 may also be a period for
displaying an image. In this case, a period from the start point of the
internal light irradiation period IL_ON to the start point of the reset
or output period SUa of the first sensing unit SUa, as a display period,
may be a period in which a gate-on voltage is applied to all of the image
scanning signal lines (not shown) in sequence so as to apply image data
voltages corresponding to image information for one screen to pixels (not
shown).

[0106] In the exemplary embodiment of the present invention, since the
reset periods SUb_r and SUb_k of the second sensing unit SUb are
positioned in the display period, the generated sensing signal may
include noise due to various driving signals for displaying. However, in
the reset periods SUb_r and SUb_k, since the second sensing unit is just
reset and the contact information is not acquired by using the sensing
signal, noise in the contact information largely does not occur. On the
contrary, as described above, since the second sensing unit SUb for
sensing the exterior light OL goes through many reset steps, the
remaining charges of the sensing element Qs activated by the internal
light IL or exterior light OL are removed and the capacitor Cs may be
sufficiently recharged to the reference voltage Vf, thereby acquiring
more exact contact information.

[0107] A blank period may be positioned between the display periods of the
adjacent frames. In the blank period, the image inputted in the
immediately preceding display period may be maintained. In the exemplary
embodiment of the present invention, the output period SUa of the first
sensing unit SUa and the output period SUb of the second sensing unit SUb
are adjacent to each other and may be positioned within the blank period.

[0108] Since an image display operation of the display device may be in
accordance with various known techniques of the art and is understood to
those skilled in the art, a more detailed description of image display is
omitted.

[0109] The driving method shown in FIG. 6 may also be applied to photo
sensors including three kinds of sensing units, or any other number, as
described above. For example, in the case where the display device
including the photo sensor according to the exemplary embodiment of the
present invention includes four kinds of sensing units SUa, SUb, SUc, and
SUd, the two sensing units SUa and SUb have a reset or output period once
for one frame like the first sensing unit SUa in the exemplary embodiment
shown in FIG. 6, and the two sensing units SUc and SUd go through
multiple reset steps and an output step for one frame like the second
sensing unit SUb in the exemplary embodiment shown in FIG. 6.

[0110] In one approach, the four adjacent sensing units SUa, SUb, SUc, and
SUd can be successively grouped into three sequential pairs, to be driven
like the first sensing unit SUa and the second sensing unit SUb shown in
FIG. 6.

[0111] For example, with respect to any first frame, the first sensing
unit SUa generates a sensing signal influenced by the internal light IL
and the exterior light OL through one reset or output period, and the
second sensing unit SUb generates a sensing signal due to the exterior
light OL through several closely-spaced reset periods and one output
period for the first frame, thereby acquiring the contact information for
the first frame.

[0112] In a second frame immediately following the first frame, the second
sensing unit SUb generates a sensing signal influenced by the internal
light IL and the exterior light OL through one reset or output period,
and the third sensing unit SUc generates a sensing signal due to the
exterior light OL through several closely-spaced reset periods and one
output period for the second frame, thereby acquiring the contact
information for the second frame.

[0113] Similarly, in a third frame immediately following the second frame,
the third sensing unit SUc generates a sensing signal influenced by the
internal light IL and the exterior light OL through one reset or output
period, and the fourth sensing unit SUd generates a sensing signal
according to the exterior light OL through several closely-spaced reset
periods and one output period for the third frame, thereby acquiring the
contact information for the third frame.

[0114] Next, a driving method of a display device including a photo sensor
according to another exemplary embodiment of the present invention will
be described with reference to FIGS. 7 and 8. Like reference numerals
designate like constituent elements as the exemplary embodiment described
above and repetitive description is omitted.

[0115]FIG. 7 is an example of a timing diagram illustrating a driving
method of a display device including a photo sensor according to another
exemplary embodiment of the present invention, and FIG. 8 is an example
of a timing diagram illustrating a driving method of a display device
including a photo sensor according to another exemplary embodiment of the
present invention.

[0116] The driving method according to the exemplary embodiment shown in
FIGS. 7 and 8 is largely the same as the exemplary embodiment shown in
FIG. 6 described above, but the number and positions of preceding reset
periods SUb_k of the second sensing unit SUb may vary.

[0117] In detail, in the exemplary embodiment shown in FIGS. 7 and 8, the
preceding reset period SUb_k of the second sensing unit SUb may include
one preceding reset period SUb_1. According to the exemplary embodiment
shown in FIG. 7, the preceding reset period SUb_1 may overlap an internal
light irradiation period IL_ON. On the contrary, according to the
exemplary embodiment shown in FIG. 8, the preceding reset period SUb_1
may not overlap the internal light irradiation period IL_ON. Further, the
preceding reset period SUb_1 and the main reset period SUb_r may be
temporally separated from each other as shown in FIG. 7 and may be
temporally continuous (i.e., one beginning immediately after the other
ends) as shown in FIG. 8.

[0118] Next, a display device including a photo sensor according to an
exemplary embodiment of the present invention and a driving method
thereof will be described with reference to FIGS. 9 and 10. Like
reference numerals designate like constituent elements as the exemplary
embodiment described above and repetitive description is omitted.

[0119]FIG. 9 is a layout view of a photo sensor according to a further
exemplary embodiment of the present invention and FIG. 10 is another
example of a timing diagram illustrating a driving method of a display
device including a photo sensor according to another exemplary embodiment
of the present invention.

[0120] Referring to FIG. 9, the display device including the photo sensor
according to this exemplary embodiment has a similar structure to the
exemplary embodiment shown in FIG. 5 described above. In detail, the
display device according to this exemplary embodiment includes a first
scanning signal line group (Ga1, Ga2, . . . ) and a second scanning
signal line group (Gb1, Gb2, . . . ) which may independently transmit
scanning signals, a first sensing unit SUa connected to the first
scanning signal line group (Ga1, Ga2, . . . ), and a second sensing unit
SUb connected to the second scanning signal line group (Gb1, Gb2, . . .
). The first sensing unit SUa and the second sensing unit SUb are
arranged in a matrix form and may be alternately disposed (i.e. disposed
in alternating manner) in a row direction and/or a column direction.

[0121] An internal circuit of the first sensing unit SUa and the second
sensing unit SUb is largely the same as the circuit shown in FIG. 2
described above, but the source voltage to which the input terminal of
the sensing element Qs of the first sensing unit SUa is connected may be
different.

[0122] In further detail, the display device according to this exemplary
embodiment of the present invention may include a first source voltage
line Vs_a and a second source voltage line Vs_b. The first and second
source voltage lines Vs_a and Vs_b may extend substantially parallel to
sensing signal lines RO1 RO2, . . . , RO m-1, Rom and may cross scanning
signal lines Ga1, Gb1, Ga2, Gb2, . . . . An input terminal of the sensing
element Qs of the first sensing unit SUa is connected with the first
source voltage line Vs_a, and an input terminal of the sensing element Qs
of the second sensing unit SUb is connected with the second source
voltage line Vs_b. As described above, the second sensing unit Sub is
used to remove noise in the signal from first sensing unit Sub resulting
from exterior light OL.

[0123] Referring to FIG. 10, a driving method of the display device
including the photo sensor according to this exemplary embodiment is
largely the same as the exemplary embodiment shown in FIG. 6 described
above.

[0124] The first source voltage line Vs_a transmits a source voltage
having a predetermined first voltage level V1 for one frame. The first
voltage level V1 may be smaller than the reference voltage Vf transmitted
through the sensing signal lines RO1, RO2, . . . . However, the voltage
of the second source voltage line Vs_b may be either the first voltage
level V1 or a second voltage level V2. The second voltage level V2 has a
larger value than the first voltage level V1 and may be the same as the
reference voltage Vf. If the reference voltage Vf is applied to the input
terminal of the sensing element Qs of the second sensing unit SUb, since
a voltage difference between the input-output terminals of the sensing
element Qs is 0 V, photocurrent may be minimized when light is
irradiated. The first voltage level V1 may be the same as a voltage level
of the bias voltage Vb which is applied to a control terminal of the
sensing element Qs.

[0125] A first period in which the voltage of the second source voltage
line Vs_b is the second voltage level V2 may overlap the internal light
irradiation period IL_ON of the backlight 900. In more detail, a width of
the first period in which the voltage of the second source voltage line
Vs_b is the second voltage level V2 may be about 75% or more and about
125% or less of a width of the internal light irradiation period IL_ON.
Further, a central axis of the first period and a central axis of the
internal light irradiation period IL_ON may coincide with each other or
may not coincide with each other, but are close to each other, such that
the first period and the internal light irradiation period IL_ON may
completely or almost completely overlap each other.

[0126] When the voltage difference between the input-output terminals of
the sensing element Qs of the second sensing unit SUb during the internal
light irradiation period IL_ON is smaller than the voltage difference
among other periods, while the internal light IL is irradiated, photo
leakage current occurring in the second sensing unit SUb may be
minimized. Then, the charge amount remaining in the sensing element Qs of
the second sensing unit SUb during the internal light irradiation period
IL_ON may be minimized from the first. Therefore, an effect due to the
remaining charge amount may be minimized in the sensing period SPb of the
second sensing unit SUb and a more exact sensing signal due to the
exterior light OL may be acquired, thereby producing more exact contact
information.

[0127] While this invention has been described in connection with what is
presently considered to be practical exemplary embodiments, it is to be
understood that the invention is not limited to the disclosed
embodiments, but, on the contrary, is intended to cover various
modifications and equivalent arrangements included within the spirit and
scope of the appended claims.